Each crystal is actually made up of silica gel a material that has a huge number of micropores in its structure meaning that is absorbs humidity and odours exceptionally well. This allows the crystals to not only absorb cat urine but to also trap the smell of ammonia leaving the air around your cats litter box fresher and cleaner. Made from silica gel Micropores in silica trap odours and absorb urine Odour control Highly absorbent Can also control the growth of bacteria Simply remove solid waste and saturated crystals when required A 6.3kg bag is equivalent to 15L and normally lasts 14 weeks